Computer
Muscle Function Analysis
15
Muscle tissues maintain electrical imbalances, or potentials, across cell membranes by
concentrating positive or negative charges on opposite sides of those membranes. These
potentials are a form of stored energy. With activation (such as from a nerve impulse), the ions
are allowed to cross the muscle cell membranes, generating electrical activity and resulting in
muscle contraction.
An electromyogram, or EMG, is a graphical recording of electrical activity within muscles. It is
useful in the diagnosis of disorders affecting muscles and the nerves that supply them. Inherited
and acquired disorders of muscles (such as the muscular dystrophies), and disorders of the central
and peripheral nervous systems (such as Huntington’s disease and diabetic neuropathy) result in
abnormal EMG readings.
EMG studies are also useful for investigating normal muscle function. In this experiment, you
will analyze electrical activity in the extensor muscles of the forearm. These muscles originate in
tendons of the proximal dorsal forearm in the region of the lateral epicondyle and attach distally
to tendons which control extension of the hand and fingers (see Figure 1). Inflammation of the
tendons at the elbow is common and can result from repetitive motions used in sports, hobbies,
and in the workplace. This experiment will demonstrate the rationale behind treating tennis
elbow with a wrist splint.
Figure 1
Important: Do not attempt this experiment if you suffer from tennis elbow or other disorders of
the arm or hand. Inform your instructor of any possible health problems that might be
exacerbated if you participate in this exercise.
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OBJECTIVES
In this experiment, you will

Obtain graphical representation of the electrical activity of a muscle.
 Associate muscle activity with movement of joints.
 Correlate muscle activity with injury.
MATERIALS
computer
Vernier computer interface
Logger Pro
Vernier EKG Sensor
electrode tabs
ruler
1–2 kg (3 lb) weight (barbell or similar)
PROCEDURE
Select one person from your lab group to be the subject.
1. Connect the EKG Sensor to the Vernier computer interface. Open the file
“15 Muscle Funct Analysis” from the Human Physiology with Vernier folder.
2. Attach three electrode tabs to your dominant arm, as shown in Figure 2. Two tabs should be
placed on the dorsal forearm, 5 cm and 10 cm from the lateral epicondyle along an imaginary
line connecting the epicondyle and the middle finger. A third electrode tab should be placed
on the upper arm.
3. Connect the EKG clips to the electrode tabs as shown in Figure 2. The red and green leads
are interchangeable for this experiment. Stand facing your table or lab bench so that your arm
is angled down toward the surface (Figure 2).
Figure 2
Figure 3
4. Rest your fingertips on the table, with your palm above the surface and in line with your
forearm, as shown in Figure 2. Click
to begin data collection. If your graph has a
stable baseline (see Figure 3), click
and continue to Step 5. If your graph has an
unstable baseline, click
and try again until you have a stable baseline for 5 s.
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Human Physiology with Vernier
Muscle Function Analysis
5. Collect data while flexing and relaxing the extensor muscle.
a. Click
.
b. After recording a stable baseline for 5 s, gently cock your hand back
as far as you can (Figure 4). Hold this position for 5 s.
c. Return your hand to its relaxed position, with fingertips resting on
the table surface, for a period of 5 s.
d. Repeat the extension and relaxation action for one more full cycle–
5 s with the hand cocked, followed by 5 s with the hand in a resting
position. Data will be collected for 25 s.
6. Store this run by choosing Store Latest Run from the Experiment menu.
Figure 4
7. Click and drag to highlight the first 5 s of data collected. Click the Statistics button, , click
the box in front of Run 1 to obtain statistics for this run, and click
. Record the
minimum and maximum values displayed in Table 1, rounding to the nearest 0.01 mV.
8. Drag the Statistics brackets to highlight each of the next 5 s intervals until you reach 20 s
(5–10 s, 10–15 s, 15–20 s). Record the minimum and maximum values displayed in the
Statistics boxes in Table 1. When you are finished, close the Statistics box by clicking the 
in the corner of the box. Note: You may have to slightly adjust the time parameters for the
data selected, as flexion and relaxation times may not conform strictly to the 5-second time
periods.
Ergonomics and Muscle Protection
9. Obtain a 1–2 kg (3 lb) weight (barbell or similar) from your instructor.
10. Place your relaxed hand on the weight, with your palm facing downward. Click
to
begin data collection. If your graph has a stable baseline, click
and continue to
Step 11. If your graph has an unstable baseline, click
and repeat data collection until
you have obtained a stable baseline for approximately 5 s.
11. Collect data to examine the effect of lifting a weight using your extensor muscles:
a. Click
.
b. After recording a stable baseline for 5 s, grip the weight with your
hand. Using only the action of your wrist, lift the weight to a
height of 5–10 cm off the surface of the table (Figure 5). Hold this
position for 5 s.
c. Gently lower the weight onto the table and rest for 5 s.
d. Repeat the extension and relaxation action for one more full cycle–
5 s with the hand cocked, followed by 5 s with the hand in a
resting position. Data will be collected for 25 s.
Figure 5
12. Store this run by choosing Store Latest Run from the Experiment menu.
13. Click and drag to highlight the first 5 s of data collected. Click the Statistics button, , click
the box in front of Run 2 to obtain statistics for this run, and click
. Record the
minimum and maximum values displayed in Table 1, rounding to the nearest 0.01 mV.
14. Drag the Statistics brackets to highlight each of the next 5 s intervals until you reach 20 s
(5–10 s, 10–15 s, 15–20 s). Record the minimum and maximum values displayed in the
Statistics boxes in Table 1. When you are done, close the Statistics box by clicking the  in
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the corner of the box. Note: You may have to slightly adjust the time parameters for the data
selected, as flexion and relaxation times may not conform strictly to the 5-second time
periods.
15. Place your hand, palm facing upwards, under the weight. Lightly grip the weight. Click
to begin data collection. If your graph has a stable baseline, click
and continue
to Step 16. If your graph has an unstable baseline, click
and repeat data collection
until you have obtained a stable baseline for approximately 5 s.
16. Collect data while lifting a weight using your flexor muscles:
a. Click
.
b. After recording a stable baseline for 5 s, using only the action of
your wrist, lift the weight to a height of 5–10 cm off the surface
of the table (see Figure 6). Hold this position for 5 s.
c. Gently lower the weight onto the table and rest for 5 s.
d. Repeat the flexation and relaxation action for one more full
cycle–5 s of flexing upward with weight, followed by 5 s with
the hand in a resting position.
Figure 6
17. Click and drag to highlight the first 5 s of data. Click the Statistics
button, , click the box in front of Run 3 to obtain statistics for this run, and click
.
Record the minimum and maximum values in Table 1, rounding to the nearest 0.01 mV.
18. Drag the Statistics brackets to highlight each of the 5-second intervals until you reach 20 s
(5–10 s, 10–15 s, 15–20 s). Record the minimum and maximum values in Table 1. Note: You
may have to slightly adjust the time parameters for the data selected.
19. Calculate the difference between each minimum and maximum value and record this value in
the data table.
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Muscle Function Analysis
DATA
Table 1
Condition
Interval
(approximate)
Fingers resting on table
0–5 s
Hand cocked back
5–10 s
Fingers resting on table
10–15 s
Hand cocked back
15–20 s
Fingers resting on weight–overhand
0–5 s
Hand cocked back with weight
5–10 s
Fingers resting on weight–overhand
10–15 s
Hand cocked back with weight
15–20 s
Fingers loosely gripping weight–underhand
0–5 s
Hand flexed upward with weight
5–10 s
Fingers loosely gripping weight–underhand
10–15 s
Hand flexed upward with weight
15–20 s
Minimum
(mV)
Maximum
(mV)
mV
DATA ANALYSIS
1. Reviewing your data, what conclusion can you reach regarding the relationship between the
strength of muscle contraction and the amplitude of electrical activity generated?
2. What do the results in Table 1 show about the relationship between hand position and muscle
activity when lifting an object?
3. What advice would you give to a friend with tennis elbow about how she should lift a frying
pan onto the stove or a can of paint onto a work bench?
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4. Using what you have learned in this experiment, explain why a wrist brace is effective
treatment for tennis elbow.
5. Some people keyboard with their wrists resting on the table or on a wrist support. In light of
what you have learned from this experiment, would you recommend this practice as a way of
preventing injury to the extensor muscles of the forearm? Why or why not?
6. Based on this experiment, what advice would you give to a beginning piano player about
proper hand position?
7. Pitcher’s elbow is a repetitive use injury of the medial epicondyle. What do the muscles that
attach to the medial epicondyle control? How would you adapt this experiment to test these
muscles?
EXTENSION
In Step 2, the leads may be placed on the ventral forearm instead of the dorsal forearm (Figure 6).
The remaining steps can then be carried out without change. Explain the resulting EMG tracing.
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